1. Field of the Invention
The present invention relates to a system and method for optimizing random access control, and for optimizing transmission efficiency of data packets over reverse common channels between access terminals and a base station, in a wireless communications system. More particularly, the present invention relates to a system and method for using inhibit sense multiple access (ISMA) protocol and a capture message to optimize random access control, and to optimize transmission of variable length/multi-frame data packets over a contention-based reverse link common channel between access terminals and a base station, in a wireless communications system.
2. Description of the Related Art
Wireless communications systems, such as wireless mobile telephone systems, include a plurality of mobile access terminals, such as mobile telephones, and a plurality of base stations (BS). Each BS provides service to a particular region on the earth""s surface, commonly referred to as a xe2x80x9ccellxe2x80x9d, to enable mobile access terminals within the cell to communicate with, for example, other mobile access terminals within that or other cells of the system, or with telephones of a PSTN network.
As can be appreciated by one skilled in the art, when a user places a call or otherwise initiates communication via a mobile access terminal, the mobile access terminal initiates communication with the BS servicing the cell in which the mobile access terminal resides by performing a random access attempt on a reverse common channel (RCCH) which the BS continuously monitors. In conventional point-to-multipoint wireless communications systems, such as wireless mobile communications systems, a protocol known as xe2x80x9cslotted ALOHAxe2x80x9d is used for the random access attempt.
In accordance with the slotted Aloha protocol, access transmission by a mobile access terminal is required to begin only at distinct periodic time instants. The timing of the periodic time instants is derived from a forward common broadcast channel transmitted by the BS to be received by all mobile access terminals within the cell being serviced by the BS. All mobile access terminals typically randomize their transmission time to one of the valid transmission instants, and transmit their access data packets on an RCCH. Hence, the mobile access terminal initiating the access attempt will randomize its transmission time to one of the valid transmission instants and transmit its access data packet on an RCCH at that time.
Immediately after the mobile access terminal has completed transmission of its access data packet, the mobile access terminal monitors the Forward Common Control Channel (F-CCCH) for a response from the BS. If the BS has successfully received the access data packet, the BS sends a response message to the mobile access terminal on the F-CCCH and, consequently, communication between the BS and the mobile access terminal is established.
Although different mobile access terminals may initiate an access attempt at about the same time, access data packets from different mobile access terminals generally will arrive at the BS in different time slots. However, depending upon the number of access terminals attempting access, more than one access data packet signal may fall within the same time slot. In a time-divisional multiple access (TDMA) based system, this collision of access data packet signals results in a failed access attempt for all access terminals whose access data packet signals occupy that time slot. On the other hand, in a code division multiple access (CDMA) based system, when two or more access data packet signals using a common access code channel fall within the same access slot, one of the access data packet signals can be xe2x80x9ccapturedxe2x80x9d (i.e. detected and demodulated) as long as the access data packet signals arrive at the access receiver of the BS more than one chip delay apart. In this event, the other non-captured access data packet signals become undesirable interference, which results in a loss in capacity and reduction in throughput in the communications system.
As can be appreciated by one skilled in the art, a conventional CDMA based communications system employing the slotted ALOHA protocol provides no mechanism to prevent access attempts from other access terminals while the captured access data packet signal is being demodulated, nor does such a system have the capability of suspending the transmissions of the other colliding access data packet signals before their entire packet transmission is completed. These deficiencies can cause significant performance degradation, especially in systems in which data is transmitted in variable size (i.e. multi-frame) packets.
Another deficiency of the slotted Aloha protocol used in IS-95B communications systems and in some other conventional communications systems is that the access terminals in these systems transmit their data packets in a fixed slot size, which is set to be equal to a fixed number of frames appropriate to accommodate the access data packet. However, as can be appreciated by one skilled in the art, using a fixed slot size for transmitting data packets of different lengths is not efficient. For example, when data packets smaller than access slot size are transmitted in respective slots, part of the slot in which each data packet is transmitted remains empty and is thus wasted. On the other hand, data packets longer than access slot size must be broken into pieces and sent in multiple access slots, which requires additional overhead bits and processing that reduces the efficiency of the system while increasing system complexity.
Accordingly, a continuing need exists for a wireless communications system having increased random access control efficiency and overall increased efficiency of data packet transmission over reverse common channels between access terminals and a base station.
An object of the present invention is to provide a system and method for optimizing random access control, and for optimizing transmission efficiency of data packets over reverse common channels between access terminals and a base station, in a wireless communications system.
Another object of the present invention is to provide a system and method for minimizing interference between access data packets being transmitted by multiple access terminals and being received in the same time slot by a base station in a wireless communications system.
A further object of the present invention is to provide a system and method for using inhibit sense multiple access (ISMA) protocol and a capture message to optimize random access control, and to optimize transmission of variable length/multi-frame data packets over a contention-based reverse link common channel between access terminals and a base station, in a wireless communications system.
These and other object of the present invention are substantially achieved by providing a wireless communications system and method for using the same, employing a plurality of access terminals and a base station, in which at least one of the access terminals is adapted to transmit at least a portion of an access data packet to the base station, and the base station is adapted to receive the portion of the access data packet and, in response, to transmit a message for receipt by the plurality of access terminals which indicates receipt of the access data packet portion by the base station. The portion of the access data packet can be the entire access data packet, and can include identifying data such as a PN-offset of an access PN-code, while the message can include data indicative of the identifying data in the portion of the access data packet. The base station is also adapted to transmit a control signal for controlling each of the access terminals, other than the access terminal from which the portion of the access data packet is received, to refrain from transmitting a respective access data packet in response to receipt of the message. The base station can further transmit a power control command to the certain access terminal from which the portion of the access data packet is received, to control a transmission power at which the certain access terminal transmits communication data to the base station. In addition, the base station can transmit a control signal to the certain access terminal to control that access terminal to transmit another portion of the data packet over the same or a different reverse common channel for receipt by the base station.